Did a Cummins conversion on a 8050 and its works great but I used the 8.3 engine.If you put in the smaller engine in that heavy a tractor and set it to around 105 hp it won't have any resale at all.You will be money ahead to just trade it for a good tractor in the power range you want.If it leaks more than it burns just fix the leaks,put in a set of main bearings and keep using it.Could even go as far as putting in rod bearings and new bolts.Doesn't sound like you strain it at all so it should last a long time.You could also have the fuel turned down to save fuel then set it back if you decide to trade it later.